The fluid transport pipe is for example disposed at the bottom of a body of water, for transporting fluid over the bed of the body of water, before the raising thereof to the surface.
The pipe is advantageously a rigid pipe formed from at least one metal tube. By way of a variant, the pipe is a flexible pipe. It is for example laid on the bottom of the body of water or/and is buried in the bed of the body of water at a shallow depth.
The fluid transported by the pipe is in particular a petroleum fluid containing hydrocarbons, such as petroleum or natural gas.
When this type of fluid is in circulation at the bottom of a body of water at great depths, the compounds present in the fluid, such as hydrates or paraffins are very prone to solidifying and forming build-ups of solids including for example constrictions and in certain critical cases plugs.
By way of a variant, the hydrates and paraffins are formed during a shut-down of production due to a maintenance operation or a malfunction.
The build-ups of solid thus formed disrupt the flow and circulation of the fluid and the operation of the installation, which could lead to significant losses in revenues for the operator of the facility.
The method generally used in the industry in order to unclog a pipe blocked by hydrates is depressurisation. Indeed, pressure being one of the conditions for formation of the hydrates, the depressurisation of the pipe over a fairly long time period helps bring about, at least partially, the elimination of plugs. The greater the degree of depressurisation the lesser the time necessary to bring about the dissociation of plugs. However, overly excessive and extremely rapid depressurisation of the interior of the pipe may cause the collapse of the pipe on to itself under the effect of external pressure, in particular but not exclusively in the case of flexible pipes.
Similarly, the column of liquid within the interior of the rising column (“riser” as per the accepted terminology) imposes a hydrostatic pressure within the interior of the pipe that is difficult to control. Thus it is impossible to depressurise below a certain threshold level imposed by this hydrostatic pressure. In practice, depending on the level of depressurisation within the interior of the pipe and the depth at which the said pipe is located, the time required for the dissociation may easily amount to several months.
In addition, this method entails collecting of the gas or liquid at the surface during the dissociation of the plugs. As a consequence thereof, in order to be performed this operation necessitates the intervention by a specialised vessel that is capable of collecting and processing these fluids in accordance with the standards stipulated in the ATEX directives, which is rare and very expensive.
In certain cases, it is also known practice to introduce into the pipe a mechanical system designed to dislodge the plugs. Operations of this type are burdensome and difficult to carry out and costly. They generally require a shut-down of the production processes. In addition, these operations can be performed only over a relatively short length and typically over the vertical part of the pipe.
Also, in critical cases, none of the conventional means prove to be effective in unblocking the pipe, thus resulting in it's becoming inoperative.
An alternative treatment device for treating plugs in a fluid transport pipe is described for example in the document U.S. Pat. No. 6,939,082. In this device, a remotely operated vehicle is lowered down to a point of the pipe at which a hydrate plug is found. A liner is disposed above the pipe, while leaving available an intermediate space. The water present in the intermediate space is heated and made to circulate in order to heat the pipe and cause the melting of the plug.
Such a device is not entirely satisfying. The operational implementation thereof is burdensome and difficult and makes it necessary to form a local seal in the intermediate space defined above the pipe. The temperature applied to the pipe is difficult to control in a precise manner. Furthermore, the location of the hydrate plug must be known a priori, prior to treating it, which requires lengthy and costly investigations.
In addition, this device provides for only highly localized treatment of the plug (typically 2 m). In the absence of data relating to the location and the length of the plug, the time periods required to perform the operations could become excessively long.
The use of such a device also carries certain risks. In effect, the generation of plugs results in an irregularity in the pressure levels along the pipe line. Thus, the pressure may be much higher on one side than on the other side of the plug. The local heating increases the problems of irregularity that can bring about the violent expulsion of the plug and cause damage to the pipe, or even create zones of overpressure that could degrade the pipe.
In addition, once the zone has been treated, if the device were to be moved for treating a new zone, there is a risk of the hydrates being possibly reformed in the zone that was initially treated during the treatment of the subsequent zone.
One object of the invention is to provide a device that makes it possible to monitor and treat effectively, in a simple and inexpensive manner, the build-ups of solid material within a fluid transport pipe submerged in a body of water.
To this end, the object of the invention relates to a cover of the aforementioned type, characterized in that the elongate body is reversibly deformable under the effect of its own weight, the elongate body having a length of more than 10 m.
The cover according to the invention may include one or more of the following characteristic features, taken into consideration in isolation or in accordance with any technically possible combination:                the elongate body has a length that is greater than 100 m, advantageously greater than 1 km;        at least one longitudinal interaction element for interacting with the pipe is a longitudinal temperature measurement sensor for measuring the temperature, that is borne by the elongate body;        the longitudinal temperature measuring sensor extends over at least 90% of the length of the elongate body;        the cover includes at least one ballast element borne by the elongate body;        the elongate body is adapted so as to be wound in a reversible manner over a rotating storage device;        the cover includes at least one longitudinal reinforcement armor borne by the elongate body;        the cover includes at least one handling element that is adapted so as to be gripped by a remotely operated underwater vehicle;        the elongate body comprises a thermally insulating material;        at least one longitudinal interaction element for interacting with the pipe is a longitudinal heating element advantageously comprising an electrical heating resistor.        
The object of the invention also relates to an operating assembly disposed to be facing a fluid transporting pipe submerged under a body of water, that comprises:                at least one cover as defined here above;        an activation, control and monitoring unit for activating, controlling and monitoring the or each longitudinal interaction element for interacting with the pipe, connected to the or each cover.        
The assembly according to the invention may include one or more of the following characteristic features, taken into consideration in isolation or in accordance with any technically possible combination:                a rotating storage device, the cover being adapted so as to be wound and unwound in a reversible manner over the rotating storage device.        
The invention also relates to an interaction method for interacting with a fluid transport pipe disposed in a body of water, that includes the following steps:                provision of a cover as defined here above;        placement of the cover in the body of water in order for it to be disposed to be facing an outer surface of the fluid transport pipe;        activation of the or each longitudinal interaction element for interacting with the pipe, so as to interact with the pipe, in particular for heating the pipe or for measuring a temperature of the pipe.        
The method according to the invention may include one or more of the following characteristic features, taken into consideration in isolation or in accordance with any technically possible combination:                the step of placement of the cover includes the application of the cover on to the outer surface of the fluid transport pipe, and the spontaneous deformation of the cover so as to fittingly adapt to the form and shape of the outer surface of the fluid transport pipe.        the pipe is at least partially buried in the bed of the body of water, the step of placement comprising of the application of the cover on to a bearing surface situated so as to be at a distance away from and facing the outer surface of the fluid transport pipe, advantageously on the bed of the body of water, and the spontaneous deformation of the cover so as to fittingly adapt to the form and shape of the bearing surface.        